Motherboard Processors and Memory

Chapter 1: Motherboards, Processors and Memory

MOTHERBOARD

Motherboard is the most important part of computer binding all the other parts together.
System boards depend on the form factor:

Advanced Technology Extended (ATX)

  • The processor and memory slots at right angles to the expansion cards.
  • We can install full-length expansion cards.

MICRO ATX

  • Micro ATX follows the ATX principle but with smaller footprint.
  • Lower power consumption, heat loss.
  • Disadvantage: lesser memory slots, headers, integrated components.

ITX

  • Low power, Small Form Factor
  • For specific uses like embedded systems

SYSTEM BOARD COMPONENTS

CHIPSETS

  • Collection of chips or circuits that perform interface and peripheral functions for the processor.
  • Dictates how a motherboard will communicate with the installed peripherals.

Northbridge:

  • Performs management of high-speed peripheral communications.
  • Responsible primarily for communications with integrated video using AGP and PCIe
  • Directly connected to southbridge and manages its connections with PC

Southbridge:

  • Slower peripherals (PS/2, parallel ports, serial ports, etc.), managing their communications with rest of the computer and the resources given to them.
  • Do not keep up with external clock of CPU
  • Motherboards today have integrated PS/2, USB, LAN, analog and digital audio for the Southbridge

EXPANSION SLOTS

Small plastic slots 1-6 in long used to install devices to expand PC’s capability.

PCI (Peripheral Component Interconnect)

  • 32-bit operates on 33/66 MHz with data rates 133/266 MBps
  • Manufactured in 3.3 and 5V versions.
  • Universal adapters are keyed to fit in slots based on either of the two voltages.

PCI-X(PCI-Extended)

  • Visibly indistinguishable
  • 64 bit bus with frequency of 133-533 MHz and data rates 4266MBps nearly 4.3 GBps

AGP (Accelerated Graphics Port)

  • Mostly used for legacy video card
  • AGP slots were designed to be a direct connection between the video circuitry and the PC’s memory.
  • Generally brown color and located next to PCI slots
  • 32 bit 66 MHz clock with data rate 266MBps
  • AGP2x, AGP4x, AGP8x further increase the clock speed by 2, 4 & 8 times respectively

PCIe(PCI Express)

  • No plug compatibility with PCI or AGP
  • Use point-to-point (P2P) communication with each component giving them certain time slots and switching between them.
  • It is a serial technology using multiple serial paths to achieve higher rates
  • Each lane connecting 2 components has a pair of wires for bidirectional communication
  • All the lanes between 2 components combine to form a link
  • 7 different link widths: x1,x2,x4,x8,x12,x16,x32 with x16 most common and the physical size also increases in that order
  • Every PCIe slot has 22-pin portion in common toward the rear of motherboard
  • 4 versions: 1.x, 2.x, 3.0 and 4.0 with data rates 250MBps, 500MBps, 1GBps, and 2GBps.
  • 500MBps bidirectional link of a x1 slot in the first version of PCIe is comparable to PCI’s best, a 64-bit slot running at66MHz and producing throughput of 533MBps
  • Combing lanes results in linear multiplication: 1 x16=4GBps which is equivalent to 16(lanes)*250(x1 rate)=4GBps and it doubles further in case of bidirectional
  • Different technologies (like SLI) allow users to combine the PCIe slots for form Single adapter.

CNR (Communication Networking Riser)

  • Made essentially for the analog processing circuitry as integrated features.
  • 60 pin slots.
  • Capabilities: Networking support, Hardware Acceleration, Plug and Play compatibility, etc.

MEMORY SLOTS

•Random Access Memory (RAM) slots hold the memory chips that make up primary memory.

•Memory chips are arranged on small circuit board like DIMM, SODIMM (for laptops) and MicroDIMMs.

•IDENTIFICATION: Black, placed closer but color coding is also available

•Number of memory slots vary but structure is similar. Plastic tabs on each side keeps the module securely in slot.

•Paging File: Virtual RAM (e.g. pagefile.sys in Windows). Reduces the performance of machine

•Cache is b/w CPU and RAM forged from sRAM. It improves the system performance by predicting the next instruction fetch. Most recent data is stored in cache. Increasing order of capacity and distance from processor die:

  • L1 cache- 64 KB in the processor
  • L2 cache- 256 KB external to processor
  • L3 cache- 4MB-12 MB in processor package but not on-die
  • RAM- 4-16 GB
  • HDD/SSD- 100-1000 GB


CPU & PROCESSOR SLOTS

•IDENTIFICATION: flat, several pins at bottom in row/column, generally square, fan/heat sink attached to it

•Sockets are different for different processors

•Top socket: Socket A Bottom socket: Socket T

•Zero Installation Force (ZIF) sockets are most popular for PGA processors

•Different locking mechanism used for LGA processors

POWER CONNECTORS
20 pin block where ATX connector plugs in.

FIRMWARE
Software encoded in hardware usually on ROM. BIOS is example.

BIOS (Basic Input/output System)
Special memory that boots the operating system & allows OS to interact with hardware. Identification is the word BIOS on chip. Offers simple interface for making selections and saving results. Can monitor the vitals like temperature, fan speed, etc.

POST
Series of system checks performed by system BIOS like size of primary memory.
After POST completion BIOS executes master boot record (MBR) and continue booting up.

CMOS Battery
PC has to save even when turned off like date, time, memory, boot sequence, etc.
Achieved using CMOS (Complementary Metal Oxide Semiconductor) memory chip as this information is stored in CMOS memory.
To prevent CMOS from losing its information, manufacturers include a small battery to power the CMOS memory.

JUMPERS AND DIP SWITCHES
These switches are used to configure various hardware options on the motherboard. But now a days not more than 1 jumper present.

FONT PANNEL CONNECTORS

Power button: Turn on/off PC,

LED’s: check that processor is working, Power is ON/OFF

Audio jack/mic: Connection to speakers and mic

USB ports: For temporary devices like cameras, etc

Reset button.

IDENTIFYING PURPOSES AND CHARACTERSTICS OF PROCESSORS

Central Processing Unit (CPU) controls & directs all activities of computer using external – internal buses. E.g. Intel, AMD.

CPU PACKAGING

  • Pin Grade Array (PGA): Square packaging found in older CPUs.
  • Dual Inline Packaging (DIP): Rectangular chips with two rows of 20 pins.

CHARACTERSTICS OF MODERN PROCESSORS

  • Hyperthreading (HTT):
    • Processors appear to OS as two processors.
    • OS can schedule 2 processes at same time using same resources.
    • Multicore: Processor exhibit completely separate processor dies in same package. E.g. Dual Core, Quad core.
    • Throttling: allows reducing the operating frequency of CPU during times of less demand/during battery operation.
    • Speed:
      • Described in clock frequency (MHz/GHz).
      • Crystal (XTL) /system clock keeps the time for the flow of data on motherboard.
      • Clock usage by frontside bus leads to an effective clock rate known as FSB speed.
      • CPU multiplies the FSB speed to produce its own internal clock rate, the third speed.
      • 32- and 64-bit processors:
        • Determines width of data that can be accessed from primary memory at a time.
        • Wider the bus, more data processed per time, more work done.
        • Virtualization support: Hardware virtualization eases the burden on the system that software-based virtualization imposes.
        • Integrated GPU:
          • Takes burden off of the CPU
          • Minimizes the amount of off-package communication that must occur
          • Improves overall system performance.

IDENTIFYING PURPOSES AND CHARACTERSTICS OF MEMORY

IMPORTANT MEMORY TERMS

  • Parity Checking /Memory Banks:
    • Parity checking
      • Error-checking scheme with no error correction.
      • Works often on 8 bits data.
      • Ninth bit is added at transmitter and removed at receiver – does not affect actual data transmitted.
    • In computers, eight memory chips form a set. A ninth chip is added to support parity bit required .These sets form memory banks.
    • Error Checking and Correction:
      • If memory supports ECC, check bits generated, stored with data.
      • Algorithm is performed on the data and its check bits whenever memory is accessed.
      • If the result is all zeros, then data is valid, processing continues.
      • Single- and Double-Sided Memory: DSM allows more computer memory using half the physical space of SSM, which requires no switching by the memory controller.
      • Single-, Dual-, and Triple-Channel Memory:
        • Single
          • classic memory model
          • Dictates only that a complete bank be satisfied whenever memory is initially installed or added.
    • Dual
      • memory controller’s coordination of two memory banks to work as a synchronized set during communication with CPU
      • Doubles the specified system bus width from memory’s perspective.
    • Triple
      • Demands the coordination of three memory modules at once.
      • Employs a form of interleaving that reduces the amount of information transferred by each module.

TYPES OF MEMORY

  • DRAM (dynamic random access memory): Requires refresh signal to retain information.
    • Asynchronous DRAM:
      • Independent from CPU’s external clock.
      • Low access time (40- 120-ns) – better overall performance.
      • Common asynchronous DRAM technologies – Fast Page Mode (FPM), Extended Data out (EDO), and Burst EDO (BEDO).
    • Synchronous DRAM:
      • Shares common clock with system bus clock.
      • Allows SDRAM to speed up with FSB, processor, eliminating the need to configure CPU for memory synchronisation.
      • Types:
        • SDR SDRAM: 1 tick = 1 bit data therefore data rate = numeric value of clock frequency.
        • DDR (Double Data Rate) SDRAM: 2 times data rate of ordinary SDRAM. Achieved by pumping date on both rising and falling edges.
        • DDR2 SDRAM: Uses lower peak voltage to keep power down also doubling the rate of DDR SDRAM (peak at 1.8 V).
        • DDR3 SDRAM: Twice as fast as DDR2 (peak at 1.5V) DR (Direct Rambus) DRAM.
  • SRAM (static):
    • No refresh required.
    • Chips are more complex, expensive, and faster.
    • SRAM is classically used for cache memory.
    • ROM (read-only):
      • Programmable ROM (PROM): could be written for once in the field using special programming device.
      • Erasable PROM (EPROM): can be erased using ultraviolet light and subsequently reprogrammed.
      • Electronically erasable PROM (EEPROM): requires slightly higher electrical pulse to erase.

MEMORY PACKAGING

  • DIMM:
    • Dual inline memory module
    • 64-bit memory modules used as a package for SDRAM family
    • RIMM:
      • custom memory module, carries DRDRAM
      • physical specification:
    • 16-bit modules – 184 pins, two keying notches.
    • 32-bit module – 232 pins, only one keying notch.
    • SODIMM (small outline DIMM): Used for notebooks and small computers.
    • MicroDIMM:
      • Newer, smaller RAM form factor.
      • Designed for ultralight portable subnotebook computer.

COOLING SYSTEMS

Electronics components produce heat where excess heat must be dissipated.

FANS

•Front Intake fan
•Rear Exhaust fan: cool power supply
•CPU fan: attached to heat sink
•Chipset fan
•Video Card Chipset fan
•Memory module fan

MEMORY/HARD DRIVE COOLING:
•Passive: cool via airflow and heat sink
•Active: Cooling medium around RAM

CPU COOLING
Generates most heat.
Have heat sensor and fan_speed_sensor to shut down processor if need arises.

AIR COOLING
CPU fan blows air down to force the heat into internal air.
Moving the heat away from the heat sink instead of pushing the air down through the heat sink is more effective.
Use of copper plates in direct contact with the CPU is very often used.
Thermal paste: compound that helps to bridge the extremely small gaps between the CPU and the heat sink, which avoids superheated pockets of air.

Advanced CPU Cooling Methods

  • Liquid Cooling:
    • Special water block is used to conduct heat away from the processor.
    • Water is circulated through this block to a radiator, where it is cooled.
    • Completely quiet.
    • Disadvantage: More expensive, complex.
    • Heat Pipes: Employ some form of tubing filled with a liquid suitable for the applicable temperature range.
    • Peltier Cooling Devices: Facilitate the transfer of heat from one side of the element, made of one material, to the other side, made of a different material. The cold side should always be against the CPU surface and the hot side should be mated with a heat sink or water block for heat dissipation.
    • Phase Change Cooling: Cooling effect from the change of a liquid to a gas is used. It is a very expensive but it does work.
    • Liquid Nitrogen/Helium Cooling: Instantaneous cooling with use of liquid nitrogen with view of setting records.
    • Undervolting: Uses property of physics whereby reduction in voltage has an exponential effect on the reduction of power consumption and associated heat production.

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